Study Guide (Ch. 8-15)

Suppose that Cepheids did not exist and there were no other standard candle technique that worked at the same distances. Which statement would be true?

We would not be able to measure the distances of distant galaxies.

Now consider the statements in Part A that are inferred from models. A solar model is used to calculate interior conditions based on certain "known" characteristics of the Sun, such the Sun's total mass. How do we know the Sun's mass?

We can calculate it by applying Newton's version of Kepler's third law with Earth's orbital period (1 year) and Earth's average distance from the Sun (1 AU).

Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?

We can learn the distance to the galaxy.

How do we know that galaxy clusters contain a lot of mass in the form of hot gas that fills spaces between individual galaxies?

We detect this gas with X-ray telescopes.

Which statement explains the observations that make it seem possible that Mars could have life underground?

We have detected water ice on Mars, and Mars still has some volcanic heat.

Which of the following is not key evidence in support of the idea that all life today shares a common ancestor?

We have identified fossils of the first life forms that ever existed on Earth.

A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call:

a gravitational lens

A standard candle is _________.

a light source of known luminosity

Why do we use Hubble's law to estimate the distances of most distant galaxies, rather than using white dwarf supernovae in all cases?

We have not observed white dwarf supernovae in most galaxies.

Stars orbiting in the ________ near the galaxy's center can have orbits highly inclined to the galactic plane.

bulge

How do scientists study the history of life on Earth?

by studying fossils, the preserved remains of past organisms

Essentially all the hydrogen nuclei that will ever exist in our universe were created __________.

by the time the universe was about 3 minutes old

How do we determine the conditions that existed in the very early universe?

We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.

Suppose you want to know what the temperature of the universe was 1 billion years ago. Where along the horizontal axis should you look?

Almost all the way to the far right.

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

Its apparent brightness will decrease by a factor of 9.

From Part B, you know that from afar you'll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why?

Its light will become so redshifted that it will be undetectable.

Which of the following places is NOT generally considered a potential home for life in our solar system?

Jupiter's atmosphere

What evidence suggests that life arises relatively easily?

Life was present on Earth soon after the end of the heavy bombardment.

During the history of the universe, what important event occurred about 380,000 years after the Big Bang?

Light began to travel freely through the universe.

Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last.

helium, carbon, oxygen, iron

In order to predict whether a star will eventually fuse oxygen into a heavier element, you mainly want to know what fact about the star?

its mass

Plants and animals are

just two small branches of the diverse "tree of life" on Earth.

Models show that the __________ of the universe is better-explained when we include the effects of dark matter along with the effects of luminous matter.

large-scale structure

If star A is closer to us than star B, then Star A's parallax angle is _________.

larger than that of star B

Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

less luminous, cooler, smaller, and less massive

Which of the following is NOT considered crucial for life to exist on some world?

liquid water

There are also two large blue-colored regions in the composite image. These blue regions are labeled as "dark matter" based on __________.

observations of gravitational lensing by the cluster

Which of the following does not provide strong evidence for the Big Bang theory?

observations of the amount of hydrogen in the universe

What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating?

observations of white dwarf supernovae

Dark energy has been hypothesized to exist in order to explain:

observations suggesting that the expansion of the universe is accelerating.

The Schwarzschild radius of a black hole depends on ________.

only the mass of the black hole

The more distant a star, the __________.

smaller its parallax angle

Looking for an Earth-size planet around a nearby star (besides the Sun) is like looking for a pinhead located _________.

thousands of kilometers away

On an H-R diagram, stellar masses _________.

can be determined for main sequence stars but not for other types of stars

This painting represents the Milky Way Galaxy as it might appear from a distance. Identify the indicated features.

from top to bottom -spiral arm -bulge -disk

Examine the visible light image of the Bullet Cluster. What kind of cluster is it?

galaxy cluster

The different time periods of the __________ are defined by changes in fossils found from those time periods.

geological time scale

A tightly packed group of a few hundred thousand very old stars is a

globular cluster

What would you expect to find in the Halo of the Milky Way Galaxy?

globular clusters

Which of the following is NOT one of the three major categories of galaxies?

globular galaxies

A __________ predicts that the strong, weak, and electromagnetic forces should become indistinguishable at high temperatures

grand unified theory

What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?

gravitational force and outward pressure

A massive object can distort the light of more distant objects behind it through the phenomenon that we call __________.

gravitational lensing

Sky surveys looking for radio signals generated by technology are part of the __________

habitable zone

The globular cluster M13 belongs to the ________ of the Milky Way Galaxy.

halo component

Which process leads to the production of carbon?

helium fusion

A solar model is used to calculate the expected temperature and density at all depths within the Sun. These results are then used to calculate the expected fusion rate within the Sun. We have confidence that the model is correct because it agrees with the observed characteristics of the Sun. Which of the following observations can be used to check that we really do know the Sun's internal fusion rate?

-Measurements of the Sun's total energy output into space -Observations of neutrinos coming from the Sun

Which of the following must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light?

-No interstellar gas or dust absorbs or scatters light between us and the star. -We have measured the star's apparent brightness. -We have measured the star's distance.

Today, most scientists accept the Big Bang theory because its predictions agree so well with observations. But a scientific theory can always be revised or discarded if future observations do not agree with its predictions. Consider the following hypothetical future observations. Which one(s) would be inconsistent with the Big Bang theory?

-Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K -Astronomers discover distant protogalactic clouds with a helium abundance below 20%. -Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today.

What evidence suggests that long gamma ray bursts originate from supernovae of stars massive enough to form black holes?

-Rapid observations in other wavelengths show that some gamma ray bursts coincide with points showing typical supernova light curves. -Some gamma ray bursts have been found to originate with galaxies that are actively forming stars, and would thus have a few very massive (but short lived) stars.

The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?

(1) The theory predicts the existence of and the specific characteristics of the observed cosmic microwave background; (2) the theory correctly predicts the observed overall chemical composition of the universe.

Shown following are the names of several eras that are used to describe the history of the universe. Rank the eras from left to right in the order in which they occurred, from first to last.

- Planck era - GUT era - electroweak era - particle era - era of nucleosynthesis - era of nuclei - era of atoms - era of galaxies

The following statements describe ways in which the analogy might apply to the real universe. Which statements are correct?

- The average distance increases with time both between raisins in the cake and between galaxies in the universe. -An observer at any raisin sees more distant raisins moving away faster, just as an observer in any galaxy sees more distant galaxies moving away faster. -The raisins stay roughly the same size as the cake expands, just as galaxies stay roughly the same size as the universe expands.

The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on their distance from Earth, from farthest to closest.

-130,000 km/s -45,000 km/s -18,730 km/s -5,264 km/s -1,577 km/s

Current estimates place the age of the universe at about _________.

14 billion years

The following figures give the approximate distances of five galaxies from Earth. Rank the galaxies based on the speed with which each should be moving away from Earth due to the expansion of the universe, from fastest to slowest.

-5 billion light-years -2 billion light-years -800 million light-years -230 million light-years -70 million light-years

If I measure the recession velocities of 2 galaxies and galaxy A has a velocity twice that of galaxy B, how far away is B if A is 100 Mpc away? (Remember that V = H0 x D)

50 Mpc

Consider all of the observations shown in the video. Which of the following are reasonable conclusions?

-Gas orbits the radio source called Sgr A*. -There are strong magnetic fields in the central region of the galaxy. -Stars near the galactic center are much closer together than stars around our Sun.

Which of the following must occur for a star's core to reach equilibrium after an initial change in fusion rate?

-If the fusion rate initially increases, then the core expands -If the fusion rate initially decreases, then the core contracts

The Chandra X-Ray Observatory has detected X rays from a star system that contains a main-sequence star of spectral type B6. The X-ray emission is strong and fairly steady, and no sudden bursts have been observed. Which of the following statements are reasonable conclusions about this system?

-The main-sequence star orbits either a neutron star or a black hole. -Gas from the main-sequence star makes an accretion disk around another object.

You should now see that the reason the mass of the star in Part A must be inferred is that the star has no known orbiting objects, which means we cannot apply Newton's version of Kepler's third law. Which of the following must be true if the star's inferred mass is to be accurate?

-We have determined that the star is a main-sequence star. -We have measured the star's spectral type.

Listed following are several locations in the Milky Way Galaxy. Rank these locations based on their distance from the center of the Milky Way Galaxy, from farthest to closest.

-a globular cluster in the outskirts of the halo -a cloud of gas and dust in the outskirts of the disk -our solar system -the edge of the central bulge

Imagine a photon of light traveling the different paths in the Milky Way described in the following list. Rank the paths based on how much time the photon takes to complete each journey, from longest to shortest.

-across the diameter of the galactic halo -across the diameter of the galactic disk -from the Sun to the center of the galaxy -across the diameter of the central bulge -through the disk from top to bottom

Different regions of the galaxy tend to contain stars of different ages. Place labels for the ages of stars in the correct regions of the galaxy painting.

-both young and old are closer to the center -mostly very old are on the outer

Listed following are several stars found in the disk and halo of the Milky Way Galaxy. Assume that both the blue and yellow disk stars are members of the same open cluster. Rank the stars based on the abundance of elements heavier than carbon that you would expect to find in each of the stars, from highest to lowest. If you expect two (or more) stars to have approximately the same abundance, rank them as equal by dragging one on top of the other(s).

-hot, blue main-sequence star in open cluster in disk & yellow main-sequence star in open cluster in disk (equal) -red main-sequence star in globular cluster M13 & red giant in globular cluster M13

The following figures show several stars found in the disk and halo of the Milky Way Galaxy. Rank the stars based on their current age, from oldest to youngest. If two (or more) stars have approximately the same age (that is, ages within a few million years), rank them as equal by dragging one on top of the other(s).

-red main-sequence star in globular cluster M13 & red giant in globular cluster M13 (equal) -the Sun -hot, blue main-sequence star in disk

Rank these times based on the wavelength of the peak intensity of the cosmic background radiation at those times, from shortest to longest. (Hint: consider how the temperature of the universe or the cosmic background radiation changed with time.)

1 million years after the Big Bang, 100 million years after the Big Bang, today

Which cosmic distance measurement techniques are considered standard candle techniques?

-white dwarf supernovae (distant standards) -main-sequence fitting -Cepheids

What happens to the core of a high-mass star after it runs out of hydrogen?

0.1 to 150 solar masses

What is the approximate range of masses that newborn main sequence stars can have?

0.1 to 150 solar masses

Approximately what is the parallax angle of a star that is 20 light-years away?

0.16 arcsecond

The horizontal axis of the graph measures the time since the Big Bang in seconds. The extreme left of the horizontal axis, where it meets the vertical axis, is labeled 10^-45 seconds (that is a decimal point followed by 44 zeroes and then a one). If we move along two tick marks to the right on the horizontal axis, it is labeled 10^-35 seconds. By what factor does the time increase from one tick mark on the horizontal axis to the next tick mark toward the right?

1 x 10^5

Suppose that you measure a galaxy's redshift, and from the redshift you determine that its recession velocity is 30,000 (3 * 10^4) kilometers per second. According to Hubble's law, approximately how far away is the galaxy?

1.4 billion light years

According to the diagram, the approximate abundance of oxygen atoms in the galaxy is __________.

1/1000 that of hydrogen

A star of spectral type G lives approximately how long on the main sequence?

10 billion years

A Cepheid with a period of 30 days has an average luminosity that is about __________ times the luminosity of the Sun.

10,000

The vertical axis of the graph measures the temperature of the universe in kelvin. If we move up one tick mark to the next, by what factor does the temperature increase?

100

How long after the Big Bang was the Planck time, the time at which our current theories become completely unable to describe conditions any earlier in the universe?

10^-43 second

What was the approximate temperature of the universe when the universe was just 1 second old?

10^10 K

Look again at the orbit of the star with the highlighted orbit. By comparing the orbit to the scale bar shown on the diagram, you can estimate that this orbit has a semimajor axis of about _____.

1150 AU

10 times Earth's distance from the Sun. Express your answer using two significant figures.

13 watts/m^2

According to the Big Bang theory, how many forces-and which ones-operated in the universe during the GUT era?

2 forces: gravity and a single force that later became the strong, weak, and electromagnetic forces

Notice that the window with the light curve also has a box that tells you the average apparent brightness of the Cepheid, which shows a value of 1.3 * 10^4. (The units are shown in the box, but you only need to focus on the numerical value.) Based on this apparent brightness and the luminosity you found in Part D, what is the approximate distance to this Cepheid?

2 million light-years

To determine the mass of the central object, we must apply Newton's version of Kepler's third law, which requires knowing the orbital period and average orbital distance (semimajor axis) for at least one star. We could consider any of the stars shown in the figure, so let's consider the star with the highlighted orbit (chosen because its dots are relatively easy to distinguish). What is the approximate orbital period of this star?

20 yr

Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 20 km/s/Mly. How fast would a galaxy 1000 Mly distant be receding from us?

20,000 km/s

Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?

3.3 Light Years

Twice Earth's distance from the Sun. Express your answer using two significant figures.

330 watts/m^2

The cosmic microwave background gives us a view of the universe when it was

380,000 years old.

The overall result of the proton-proton chain is that __________.

4 H becomes 1 He + energy

When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was

4 billion years old.

Based on the measurements discussed in part D, the mass of the central black hole is calculated to be about __________ times that of the Sun.

4 million

The following equation, derived from Newton's version of Kepler's third law, allows us to calculate the mass (M) of a central object, in solar masses, from an orbiting object's period (p) in years and semimajor axis (a) in astronomical units: M=a^3/p^2 Using this formula with the values you found in Parts C and D, what is the approximate mass of the central object?

4 million solar masses

To get your bearings on the horizontal time axis of this plot, it is useful to calculate the age of the universe in seconds today. If you multiply the age of the universe in years by the number of seconds in a year, approximately what is the current age of the universe in seconds?

4 x 10^17 s

According to modern science, approximately how old is the Sun?

4.5 billion years old

Shown following are several times in the history of the universe. Imagine that you were able to watch a single photon that has been part of the cosmic microwave background since it first became present in the universe. Rank these times from left to right based on the wavelength this photon would have at each time, from shortest to longest.

500,000 years after the Big Bang, 1 million years after the Big Bang, 100 million years after the Big Bang, 1.5 billion years after the Big Bang, today

Shown following are several times in the history of the universe. Rank these times from left to right based on the peak wavelength in the spectrum of the cosmic microwave background, from shortest to longest.

500,000 years after the Big Bang, 1 million years after the Big Bang, 100 million years after the Big Bang, 1.5 billion years after the Big Bang, today

Half Earth's distance from the Sun. Express your answer using two significant figures.

5200 watts/m^2

What is the approximate luminosity of the Cepheid whose light curve is shown in the graph?

8000 Lsun

Suppose a collision strips gas out of a spiral galaxy. Why would this tend to change the spiral galaxy into an elliptical galaxy?

A Galaxy cannot have a disk if it does not have gas

What is the earliest time in the universe that we can directly observe?

A few hundred thousand years after the Big Bang

What is the definition of a habitable world?

A habitable world contains the basic necessities for life as we know it, including liquid water.

Which of these stars is the most massive?

A main-sequence A star

Which of these stars has the largest radius?

A supergiant M star

Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?

A white dwarf supernova

A(n) __________ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star.

Accretion disk

How is an X-ray burst (in an X-ray binary system) similar to a nova?

Both involve explosions on the surface of stellar corpse.

The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened?

Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s.

Which of these binary systems is most likely to contain a black hole?

An X-ray binary containing an O star and another object of equal mass

Listed below are the names, spectral types (in parentheses), and approximate masses of several nearby main-sequence stars. Rank the stars based on the distances to their habitable zones (from the central star), from shortest to longest.

Barnard's star (M4), 61 Cygni A (K5), Alpha Centauri A (G2), Sirius (A1), Spica (B1)

Consider the hypothetical observation "Irregular galaxies outside the Local Group are moving toward us." From Part A, this observation would contradict the idea of an expanding universe. Why?

Because Hubble's law predicts that all galaxies outside our Local Group should be moving away from us.

Why does the rotation curve for the solar system show speeds that become slower with increasing distance from the Sun?

Because the Sun contains most of the mass of the solar system

Consider the observation "The Andromeda Galaxy, a member of our Local Group, is moving toward us." Why doesn't this observation contradict the idea that the universe is expanding?

Because the galaxies of the Local Group are gravitationally bound together.

How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?

By applying Newton's version of Kepler's third law to the orbits of the sun or other nearby stars around the center of the Galaxy

In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thus putting to rest the idea that it might have been a cloud within our own galaxy. How was he able to prove this?

By observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation.

Why are Cepheid variable stars good distance indicators?

Cepheid stars period is related to their luminosity. With that you can find its apparent magnitude and with that you can find distance. OR They have a set period - luminosity relationship

Which technique is the most useful for measuring the distance to a galaxy located 10 million light-years away?

Cepheids

To get started, click on the blue Cepheids link on the main screen of the Interactive Figure. The Interactive Figure (in red) shows a graph of the Cepheid period-luminosity relation. This graph indicates that __________.

Cepheids with longer periods have higher luminosities

How does a black hole form from a massive star?

During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.

Which of the following best sums up current scientific thinking about the nature of dark energy?

Dark energy probably exists, but we have little (if any) idea what it is.

Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies?

Dark matter is the dominant form of mass in both clusters and in individual galaxies.

Each item below belongs either with the population of disk stars or the population of halo stars of the Milky Way Galaxy. Match each item to the appropriate population.

Disk stars (yellow) -high-mass stars -youngest stars -stars that all orbit in nearly the same plane -the Sun Halo stars (green) -globular clusters -oldest stars -stars whose orbits can be inclined at any angle -stars with the smallest abundance of heavy elements

Dr. X believes that the Hubble constant is H0 = 20 km/s/Mly while Dr. Y believes it is H0 = 24 km/s/Mly. Which statement below automatically follows?

Dr. X believes that the universe is older than Dr. Y believes.

The __________ is designed as a way of estimating the number of intelligent civilizations in the Milky Way.

Drake equation

What is the cause of stellar parallax?

Earth's orbit around the sun

The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of __________.

Electron degeneracy pressure

Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?

Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars.

Astronomers suspect that a galaxy's type can be affected both by the conditions in the protogalactic cloud from which it forms ("initial conditions") and by later interactions with other galaxies. Each item below describes either a condition in a protogalactic cloud or a later interaction. Match these items to the galaxy type you would expect to form as a result.

Elliptical Galaxy - stars form rapidly as the protogalactic cloud shrinks - protogalactic cloud has high density - a galaxy collision strips away gas - protogalactic cloud rotates very slowly Spiral Galaxy - most protogalactic gas settles into a disk - protogalactic cloud has high angular momentum

It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy. Why?

Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distances from the centers of spiral galaxies.

Although we know less about dark matter in elliptical galaxies than in spiral galaxies, what does current evidence suggest?

Elliptical galaxies probably contain about the same proportion of their mass in the form of dark matter as do spiral galaxies.

Astronomers suspect that a galaxy's type can be determined either by initial conditions in a protogalactic cloud or by later interactions between galaxies. Each item below describes either an initial condition or a later interaction. Match these items to the galaxy type expected to form as a result.

Elliptical galaxy -stars form rapidly as the protogalactic could shrinks -protogalactic cloud has high density -a galaxy collision strips away gas -protogalactic cloud rotates very slowly Spiral galaxy -most protogalactic gas settles into a disk -protogalactic cloud has high angular momentum

The three types of galaxies are called:

Elliptical, Spiral and Irregular.

_________ are defined as subatomic particles that have more mass than neutrinos but do not interact with light.

WIMPs

Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances.

False

High angular momentum leads to faster rotation. Why does faster rotation tend to lead to a spiral galaxy, rather than an elliptical galaxy?

Faster rotation leads to collisions among gas particles that cause the gas to settle into a spinning disk, rather than a more spread out cloud.

From Part C, you know that in basic terms, the graph shows that the temperature of the universe decreases with time. In more specific terms, this graph shows that the temperature of the universe __________.

Fell very rapidly when the universe was young, but is changing very gradually today.

This painting represents the Milky Way Galaxy as it would appear edge-on from a distance. Label the indicated features; be sure to pay attention to where the leader lines are pointing.

From left to right, top to bottom -globular clusters -bulge -halo -disk -disk

Why should galaxy collisions have been more common in the past than they are today?

Galaxies were closer together in the past because the universe was smaller.

__________ was a dramatic expansion of the universe thought to have occurred when the universe was only a tiny fraction of a second old.

Inflation

Which of these galaxies is most likely to be oldest?

a galaxy in the local group

What do we mean when we say that the rotation curve for a spiral galaxy is "flat"?

Gas clouds orbiting far from the galactic center have approximately the same orbital speed as gas clouds located further inward.

Which method of energy generation provides the source of energy for a 10 M Sun main-sequence star?

H fusion by the CNO cycle

How did Edwin Hubble measure the distance to the Andromeda Galaxy?

He applied the period-luminosity relation to Cepheid variables in Andromeda

Listed following are characteristics that describe either high-mass or low-mass stars. Match these characteristics to the appropriate category.

High Mass -have higher fusion during main sequence life -end life as a supernova -late in life fuse carbon into heavier elements Low Mass -the sun is an example -final corpse is a white dwarf -have longer lifetimes -end life as a planetary nebula

Which of the following is a valid way of demonstrating parallax for yourself?

Hold of your hand in front of your face, and alternately close your left and right eyes

Consider the portion of the video that starts with the all-sky view of the Milky Way and then zooms in to the galactic center. All of the images except the first two show radio, infrared, or X-ray light. Why don't these images show visible light?

Interstellar dust in the galactic disk prevents us from seeing the galactic center with visible light

Why is iron significant to understanding how a supernova occurs?

Iron cannot release energy either by fission or fusion.

Which of the following is not an observed characteristic of the cosmic microwave background?

It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.

Based on what you have learned, which of the following best describes the meaning of Hubble's constant?

It describes the expansion rate of the universe, with higher values meaning more rapid expansion.

You want to determine whether a mystery object is a neutron star or a white dwarf. Which of the following properties would demonstrate that it is definitely a neutron star?

It dims and brightens more than twice per second.

What makes us think that the star system Cygnus X-1 contains a black hole?

It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star.

Why do we call dark matter "dark"?

It emits no radiation that we have been able to detect.

What happens to gas as it freely expands?

It gets less dense and cools.

Which of the following best summarizes what we mean by dark energy?

It is a name given to whatever is causing the expansion of the universe to accelerate with time.

How does the habitable zone around a star of spectral type G compare to that around a star of spectral type M?

It is larger.

What do we mean by the singularity of a black hole?

It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.

What do we mean by the star-gas-star cycle?

It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.

What do we mean by the event horizon of a black hole?

It is the point beyond which neither light nor anything else can escape.

Which of the following statements about the cosmic background radiation is not true?

It is the result of a mixture of radiation from many independent sources, such as stars and galaxies that formed within the first billion years of the Big Bang.

Which statement about the cosmic microwave background is NOT true?

It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.

Which statement about the cosmic microwave background is not true?

It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.

What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?

It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.

Given that the fossil record provides the key evidence for evolution, what is the importance of the theory of evolution?

It represents our understanding of the process by which evolution occurs.

What is the ultimate fate of an isolated white dwarf?

It will cool down and become a cold black dwarf.

The items below describe worlds or selected localities on worlds. Based on our current scientific understanding, match these items to the appropriate category below.

Likely to be habitable - underground on Mars - subsurface ocean on Europa - moon with atmosphere orbiting Jovian planet 1 AU from 1 Msun star Unlikely - surface of Mars - surface of terrestrial planet 10 AU from 0.5 Msun star - volcanoes on Io

Hubble's law is a relationship between galaxy speeds and galaxy distances. This relationship can be shown as a line on a graph of speed versus distance. Each of the following four graphs shows a possible relationship expressing Hubble's law. Rank the graphs based on their predictions of the speed, from fastest to slowest, for a galaxy located 400 million light-years away from Earth.

Line sloping downward

The table in the video shows you the speeds of Raisins 1, 2, and 3 as measured from the Local Raisin. Suppose instead that you measured speeds as seen from Raisin 2. An observer at Raisin 2 would measure __________.

Local Raisin speed = 4.0 cm/hr; Raisin 1 speed = 2.0 cm/hr; Raisin 3 speed = 2.0 cm/hr

A(n) __________ occurs when fusion creates iron in the core of a star.

Massive star supernova

What is the key observation needed to determine whether the compact object in Part C is a neutron star or a black hole?

Measure Doppler shifts in the spectrum of the main-sequence star so that you can determine the mass of the compact object.

Molly measures a Hubble constant of 20 km/sec/million light-years. Sam measures a Hubble constant of 25 km/sec/million light-years. All other assumptions being the same, which person would estimate a LARGER age to the universe?

Molly

What additional data would be most valuable in helping scientists evaluate whether the accelerating model really is the best of the four models?

More observations of very distant white dwarf supernovae

Which of the following best sums up current scientific thinking about the nature of dark matter?

Most dark matter probably consists of weakly interacting particles of a type that we have not yet identified.

During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?

Most matter was annihilated by antimatter.

The following items describe observational characteristics that may indicate that an object is either a neutron star or a black hole. Match each characteristic to the correct object; if the characteristic could apply to both types of object, choose the bin labeled "Both neutron stars and black holes."

Neutron star only -may emit rapid pulses of radio waves. -may be in a binary system that undergoes X-ray bursts. Black hole only -is detectable only if it is accreting gas from other objects. -can have a mass of 10 solar masses. Both -may be located in an X-ray binary. -may be surrounded by a supernova remnant.

Listed following are several fictitious stars with their luminosities given in terms of the Sun's luminosity (LSun) and their distances from Earth given in light-years (ly). Rank the stars based on how bright each would appear in the sky as seen from Earth, from brightest to dimmest. If two (or more) stars have the same brightness in the sky, show this equality by dragging one star on top of the other(s).

Nismo, Shelby and Ferdinand (overlapping), Enzo, Lotus

Listed following is the same set of fictitious stars given in Part A. Rank the stars based on how bright each would appear in the sky as seen from Jupiter, from brightest to dimmest.

Nismo, Shelby and Ferdinand (overlapping), Enzo, Lotus

As noted in the Introduction, some scientists have proposed that dark matter does not really exist. According to this view, all matter is ordinary (baryonic), but at large distances from matter, gravity does not precisely obey either Newton's or Einstein's theories of gravity. Is this alternative view of gravity consistent with what we observe in the Bullet Cluster? Why or why not?

No. If all matter was ordinary, then the blue region representing the location of most of the matter would line up with the red region representing the hot gas.

Each item below describes an observation of a hypothetical supernova. Classify each observation as either "Not surprising" if it fits in with our current understanding of supernovae, or "Surprising" if the observation would cause us to rethink our understanding of supernovae.

Not surprising -A white dwarf supernova in a galaxy of only old stars. -Two massive star supernovae occur in the same young star cluster. -A massive star supernova leaves behind no detectable compact object. -A massive star in a binary system explodes. Surprising -An isolated star like our Sun explodes as a white dwarf supernova. -A young (5 million years) star explodes as a white dwarf supernova.

Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit?

Nothing—Earth's orbit would remain the same.

A(n) __________ occurs when hydrogen fusion ignites on the surface of a white dwarf in a binary system.

Nova

What would stars be like if hydrogen had the smallest mass per nuclear particle?

Nuclear fusion would not occur in stars of any mass.

From hottest to coolest, the order of the spectral types of stars is _________.

OBAFGKM

Which of the following statements about asteroids, Kuiper belt objects, and Oort cloud objects is true?

Objects in the asteroid belt and Kuiper belt orbit the Sun in nearly the same plane as the planets, but objects in the Oort cloud do not.

Classify each statement below as an observation or as an inference based on the current Big Bang model. (Note that the helium abundance is defined as the mass of helium relative to the mass of hydrogen.)

Observation -Large-scale structures look about the same in all directions. -The temperature of the cosmic microwave background varies slightly with direction. -The cosmic microwave background temperature is 2.73 K. -The helium abundance is at least 25% in every galaxy studied so far. Inference -Photons of the cosmic microwave background have traveled through space for almost 14 billion years. -The cosmic microwave background is radiation left over from the big bang. -Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium. -Large-scale structure grew around density variations present in the early universe.

To understand the interplay of observations and models you must first be able to distinguish between things that we observe and things that we infer from models. Consider the following statements about the Sun. Classify each statement as an observation or as an inference based on the current, accepted model for the Sun.

Observations -The photosphere is made mostly of hydrogen and helium -The photosphere emits mostly visible light. -The corona is hotter than the photosphere. -The Sun emits neutrinos. Inferences from a model -The Sun generates energy by fusing hydrogen into helium in its core. -The convection zone is cooler than the radiation zone. -The composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system. -The core temperature is 10 million K.

Consider a relatively nearby, single star, that is, a star that is not a member of a binary system and has no known orbiting planets. Listed below are a few properties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and instruments such as cameras or spectrographs) or something that we must infer indirectly (and hence is correct only if all of our assumptions are correct).

Observe directly -color -parallax angle -spectral type -apparent brightness Infer directly -mass -surface temperature -luminosity -radius

__________ forces us to think about why the sky is dark at night.

Olbers' paradox

Suppose that our Sun was cool enough to include Mercury in its habitable zone. Which of the following would be true in that case?

Only Mercury would be in the Sun's habitable zone.

Shown following are the same eras shown in Part A. Rank the eras from left to right based on the temperature of the universe during each one, from coolest to hottest.

Opposite order of previous

The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on the amount of redshift that would be observed in each galaxy's spectrum, from largest to smallest.

Same as previous

Which of the following statements can NOT be tested by science today?

Prior to the Planck time, our universe emerged from another universe.

Each item following is a characteristic of a one-solar-mass star either during its protostar phase or during its main-sequence phase. Match the items to the appropriate phase.

Protostar Phase -luminosity much greater than the sun -radius much larger than the sun -pressure and gravity are not precisely balanced -energy generated by gravitational contraction Main-Sequence Phase -energy generated by nuclear fusion -lasts about 10 billion years -surface radiates energy at same rate that core generates energy

Note that an observer located at the Local Raisin would see Raisins 1, 2, and 3 all move away from her during the video. What would an observer located at Raisin 2 see?

Raisin 1 and Raisin 3 both move away from her.

The following figure shows how four identical stars appear in the night sky seen from Earth. The shading is used to indicate how bright (white) or dim (dark gray) the star would appear in the sky from Earth. Rank the stars based on their distance from Earth, from farthest to closest.

Rank pictures from darkest to lightest

High density tends to lead to more rapid star formation in a protogalactic cloud. Why does this rapid star formation tend to lead to an elliptical galaxy, rather than a spiral galaxy?

Rapid star formation means that there may not be enough gas left to make a disk.

Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.

Red or supergiant stars -very cool but very luminous -found in the upper-right of the H-R diagram Main-sequence stars -the majority of stars in our galaxy -the Sun, for example -the hottest and most luminous stars White dwarfs -not much larger in radius than Earth -very hot but very dim

Sirius is a star with spectral type A and Rigel is a star with spectral type B. What can we conclude?

Rigel has a higher surface temperature than Sirius.

If you wanted to observe the center of our galaxy, you would need to point a telescope in the direction of the constellation __________.

Sagittarius

Shown following are the same eras shown in Parts A and B. Rank the eras from left to right based on the size of the observable universe during each one, from smallest to largest.

Same as first related question

Consider again the same set of five stars. This time, rank the stars based on the size (width) of their habitable zones, from smallest to largest.

Same as previous

Imagine that each of the five stars is orbited by a terrestrial planet at a distance of 1 AU (Earth's distance from the Sun). Rank the stars based on the planet's expected surface temperature (not including any greenhouse effect), from lowest to highest.

Same as previous

The following diagrams are similar to those from Part B, with each diagram showing the position of "your galaxy" and another galaxy at an early and later time in the history of the universe. Rank the diagrams based on the speed at which the other galaxy is moving away from your galaxy as the universe expands, from fastest to slowest.

Same as previous

Listed following are events or phenomena that occur during either the part of the sunspot cycle known as solar minimum or the part known as solar maximum. Match these items to the correct part of the sunspot cycle.

Solar maximum -orbiting satellites are most at risk -solar flares are most common -occurs about 11 years after a solar maximum (on average) -sunspots are most numerous on the Sun -auroras are most likely in Earth's skies Solar minimum -occurs about 5 to 6 years after a solar maximum (on average)

Which of the following important events occurred earliest in the history of the universe?

Space-time rapidly expanded during a brief period of inflation.

Following are a number of distinguishing characteristics of spiral and elliptical galaxies. Match each characteristic to the appropriate galaxy type.

Spiral galaxies -have a flattened disk of stars -are rare in central regions of galaxy clusters -contain many bright, hot stars -contain abundant clouds of cool gas and dust -have significant, ongoing star formation Elliptical galaxies -are more reddish in color -contain primarily old, low-mass stars

In Part D, you saw that elements with even atomic numbers tend to be more abundant than neighboring elements with odd atomic numbers. What nuclear process explains why this is the case?

Starting from carbon (atomic number is 6), the most common nuclear reactions involve the fusion of an additional helium nucleus.

Open the Rotation Curve of a Spiral Galaxy interactive figure and click at various distances from the galactic center to create a graph of the galaxy's rotation curve; be sure to start with points very close to the galactic center and continue to well beyond the visible part of the galaxy. Which of the following statements best describes the pattern of the graph?

Starting from the center, speeds at first rise rapidly, and then become nearly constant with increasing distance.

Which of the following three-step processes correctly describes how we use Cepheids as a tool to make cosmic distance measurements? In all cases, assume that the Cepheid's apparent brightness has been carefully measured through observations.

Step 1: Measure the period of the Cepheid's brightness variations. Step 2: Use the period-luminosity relation to determine the Cepheid's luminosity. Step 3: Calculate the Cepheid's distance from its luminosity and apparent brightness.

Consider the following hypothetical observations, some of which are real and some of which are fictional. For each observation, your job is to answer this question: If the observation were real, would it provide evidence for or against the idea that the universe is expanding? Sort each observation into the appropriate bin as follows: -Place an observation in the "Supports the expanding universe" bin if it would provide evidence that the universe is expanding. -Place an observation in the "Contradicts the expanding universe" bin if it would provide evidence that would force us to reconsider the idea of an expanding universe. -Place an observation in the "Neither supports nor contradicts" bin if it does not allow us to distinguish between a universe that is expanding and a universe that is not expanding.

Supports the expanding universe -all galaxies in the Coma cluster of galaxies have redshifted spectra -the measured rate of expansion is the same in all directions -galaxies 200 million light-years away move away from us twice as fast as galaxies 100 million light-years away Contradicts the expanding universe -irregular galaxies outside the Local Group are moving toward us -spiral galaxies move away from us 10% faster than elliptical galaxies at the same distance -galaxy speeds are faster in summer than in winter Neither supports not contradicts -the Andromeda Galaxy, a member of our Local Group, is moving toward us

From Parts A though C, you should understand the three major components shown in the composite Bullet Cluster image. Notice that the hot, X-ray-emitting gas (red) is not in the same place as most of the visible galaxies and most of the matter (blue). How do we think the hot gas came to be in a different place from the galaxies and most of the matter?

The Bullet cluster is actually two separate galaxy clusters that have collided, stripping out hot gas in the process.

What actually causes a Cepheid to vary in apparent brightness?

The Cepheid varies in radius, and its luminosity is greater when its radius is larger.

Before we can use parallax to measure the distance to a nearby star, we first need to know __________.

The Earth-Sun distance

What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?

The Sun's core would start to heat up, and the rate of fusion would increase even more.

The observational data for the element abundances agree quite well with what we expect based on our current understanding of nuclear fusion and stellar evolution. But imagine the data had turned out to be different. Which of the following differences, if it had actually been observed, would have forced us to rethink our entire picture of stellar evolution?

The abundance of elements heavier than uranium turned out to be greater than the abundance of carbon.

Which of the following statements best describes what astronomers mean when they say that the universe is expanding?

The average distance between galaxies is increasing with time.

What happens when a particle of matter meets its corresponding antiparticle of antimatter?

The combined mass of the two particles is completely transformed into energy (photons).

What happens when a main-sequence star exhausts its core hydrogen fuel supply?

The core shrinks while the rest of the star expands.

One statement about the Sun from Part A is "The corona is hotter than the photosphere." Which of the following statements provides observational evidence for this claim?

The corona primarily emits X rays while the photosphere primarily emits visible light.

Which of the following hypothetical observations, if true, would disprove a prediction of the Big Bang theory?

The discovery of a galaxy with 10% helium abundance.

Like any scientific theory, the theory of evolution is subject to revision or even to being discarded if future observations do not agree with its predictions. Which of the following hypothetical observations (none of which are real or likely) would force us to reconsider the theory of evolution?

The discovery of fossils of human-like primates dating to a time before the earliest dinosaurs existed.

Scientists think it is very unlikely that complex and large forms of life could evolve on planets that orbit stars that are much more massive than the Sun. Why?

The expected lifetime of a massive star is too short to allow for the evolution of complex life

Which of the following observations cannot be explained by the Big Bang theory unless we assume that an episode of inflation occurred?

The fact that temperature of the cosmic microwave background is almost the same everywhere.

The idea that life evolves through time was first suggested in ancient Greece, and it was favored by at least some scientists of the 18th and 19th centuries even before Charles Darwin proposed the theory of evolution. What is the key observational evidence that supports the idea that life on Earth has evolved through time?

The fossil record, revealed in geological layers of different ages, shows that life on Earth has become more complex over time

Why don't we expect to find life on planets orbiting high-mass stars?

The lifetime of a high-mass star is too short.

What does Hubble's law tell us?

The more distant a galaxy, the faster it is moving away from us.

You are studying a mystery compact companion to an evolved star, with mass transfer happening. Which of the following properties suggests that the companion is definitely a black hole?

The mystery companion has a mass of over 3 solar masses.

Based on observations, which of the following statements about stars in the Milky Way is generally true?

The older the star, the lower its abundance of heavy elements.

Imagine what would happen if Jupiter were suddenly replaced by a black hole with the same mass as Jupiter.

The orbits of the solar system would be unaffected (including Jupiter's).

Which of the following models best explains why our galaxy has spiral arms?

The spiral arms are a wave of star formation caused by a wave of density propagating outward through the disk of the galaxy.

Which of the following best explains why a higher-mass cluster of galaxies causes light from a distant galaxy to bend more than a lower-mass cluster of galaxies?

The stronger gravity of a larger cluster curves space itself by a greater amount, and light follows the curvature of space.

Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster?

The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass.

The following diagrams are similar to those from parts B and C, with each diagram showing the position of "your galaxy" and another galaxy at an early and later time in the history of the universe. In this case, however, the location of the other galaxy can vary on which side of your galaxy it is from one diagram to another. Rank the diagrams based on the speed at which the other galaxy is moving away from your galaxy as the universe expands, from fastest to slowest. If two (or more) of the diagrams show galaxies moving at the same speed, show this equality by dragging one diagram on top of the other(s). (Hint: Notice that two of the diagrams show the galaxies separated by one distance and two of the diagrams show them separated by a different distance; that is, there are only two different distances shown among the four diagrams.)

The two with points farthest apart are fastest (on top of each other); and the two with points closest together are slowest (on top of each other)

Which of the following is not consistent with observations of the cosmic microwave background?

The universe is at least 20 billion years old.

In basic terms, what does the graph show?

The universe is getting cooler with time.

Which of these options is the best explanation for why the night sky is dark?

The universe is not infinite in space.

Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?

The white dwarf will explode completely as a white dwarf supernova.

What type of visible light spectrum does the Sun produce?

an absorption line spectrum

Here is Fermi's Paradox: Plausible arguments suggest that civilizations should be common. For example, even if only 1 in 1 million stars gets a civilization at some time we should see 100,000 civilizations! Which one of these are NOT plausible solutions?

There are aliens among us and we are actually in the Matrix

Although most astronomers assume dark matter really exists, there is at least one other possible explanation for the phenomena attributed to dark matter. What is it?

There could be something wrong or incomplete with our understanding of how gravity operates on galaxy-size scales.

Based on the diagram, which of the following statements best describes the observed pattern of abundances for elements with an atomic number between 6 and 20?

There is a general trend of decreasing abundance with increasing atomic number, but elements with even atomic numbers tend to be more abundant than those with odd atomic numbers.

Why is it so hard to see the bulge at the middle of the Milky Way galaxy with visible light?

There is a lot of gas and dust in the way.

You've now found that the central object has a mass of about 4 million solar masses but is no more than about 70 AU in diameter—which means it cannot be much larger than the size of our planetary system. Why do these facts lead astronomers to conclude that the central object is a black hole?

There is no known way to pack so much mass into such a small volume without it collapsing into a black hole.

Given that white dwarf supernovae are such good standard candles, why don't we use them to measure the distance to all galaxies?

They are rare events, so we have observed them in only a tiny fraction of all galaxies.

What happens when a proton collides with an antiproton?

They convert into two photons

How do astronomers use the Hubble Constant (H0) to estimate the age of the universe?

They inverse of H0 is the approximate age of the universe

What do halo stars do differently from disk stars?

They orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.

What do we mean when we say that particles such as neutrinos or WIMPs are weakly interacting?

They respond to the weak force but not to the electromagnetic force, which means they cannot emit light.

How do scientists determine the age of fossils?

They use radiometric dating to measure the age of the surrounding rocks.

Imagine that radar had never been invented and that we instead had to rely on a less reliable method of measuring distances in our solar system. If that method led us to underestimate the Earth-Sun distance by 10%, how would it affect other measurements in the distance chain?

They would all be off by the same 10%.

From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole?

Time runs increasingly slower as the rocket approaches the black hole.

True or false: light escaping from white dwarfs will show a gravitational redshift.

True

What are the three final options for a star when it dies?

White Dwarf, Black Hole, and Neutron Star

White Dwarf supernovae are created by:

White Dwarfs accreting mass and then exploding

Listed following are distinguishing characteristics of different end states of stars. Match these to the appropriate consequence of stellar death.

White dwarf -in a binary system, it can explode as a supernova. -has mass no greater than 1.4 M Sun. -typically about the size (diameter) of Earth. -supported by electron degeneracy pressure. Neutron star -sometimes appears as a pulsar. -usually has a very strong magnetic field. Black hole -viewed from afar, time stops at its event horizon. -size defined by its Schwarzschild radius.

The following items describe observational characteristics that could indicate that an object is either a white dwarf or a neutron star. Match each characteristic to the correct object.

White dwarf -may be surrounded by a planetary nebula. -emits most strongly in visible and ultraviolet. -may be in a binary system that undergoes nova explosions. Neutron star -may be in a binary system that undergoes X-ray bursts. -can have a mass of 1.5 solar masses. may be surrounded by a supernova remnant. -may repeatedly dim and brighten more than once per second.

A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the __________.

White dwarf limit

Match the items below with the correct type of supernova.

White dwarf nova -Can only occur in a binary system. -Spectra always lack strong hydrogen lines. -Can occur in a very old star cluster. -Star explodes completely, leaving no compact object behind. -Has a brighter peak luminosity. Massive star nova -Black hole or neutron star left behind. -Can only occur in a galaxy with ongoing star formation.

A(n) __________ can occur only in a binary system, and all such events are thought to have the same luminosity.

White dwarf supernova

Although we can divide the history of the universe into many distinct "eras," sometimes it's useful just to have a broad perspective on what events occurred in the very early universe and what events occurred later. Listed following are events that occurred either before or after the first five minutes in the history of the universe. Match these events to the appropriate time period.

Within the first five minutes -antielectrons (positrons) as common as electrons -temperature fell to 10^15 K -strong force and electroweak force first became distinct -inflation occurred Sometime after the first five minutes -galaxies formed -photons of cosmic microwave background released -carbon nuclei formed by fusion -stars formed

Study the composite image of the Bullet Cluster, as well as the animations. What do the two large, red-colored regions in the composite image represent?

X-ray emission from hot gas

In Part A you found that the terrestrial planet 10 AU from a 0.5MSun star is unlikely to be habitable. Could this planet be habitable if it were in a different orbit around its star?

Yes, but it would have to be less than 0.5 AU from its star.

Based on the observational evidence, is it possible that dark matter doesn't really exist?

Yes, but only if there is something wrong with our current understanding of how gravity should work on large scales.

Today, the evidence that we live in an expanding universe is extremely strong because astronomers have measured the motions of millions of galaxies. Nevertheless, in science, we must always remain open to the possibility that some future observation could call even our most strongly supported theories into question. Which of the following hypothetical observations would not be consistent with what we expect in an expanding universe?

You discover an extremely distant galaxy that is moving toward us.

Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.

a blue white dwarf star, Sun, an orange main-sequence star, a red supergiant star

What is a mutation?

a change in a living cell's DNA

Which of these star clusters is oldest?

a cluster whose brightest main-sequence stars are yellow

What kind of gas cloud is most likely to give birth to stars?

a cold, dense gas cloud

Consider a distant galaxy located directly behind a cluster of galaxies, as shown in this interactive figure. As seen from Earth, the gravitationally lensed images of the distant galaxy will appear more widely separated if the intervening cluster of galaxies has __________.

a relatively high mass and is located relatively near Earth.

Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.

a shorter wavelength

A typical neutron star is more massive than our Sun and about the size (radius) of ________.

a small asteroid (10 km in diameter)

A typical neutron star is more massive than our Sun and about the size (radius) of _________.

a small asteroid (10 km in diameter)

What do we mean by inflation?

a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence

Listed following are several astronomical objects. Rank these objects based on their mass, from largest to smallest. (Be sure to notice that the main-sequence star here has a different spectral type from the one in Part A.)

a typical black hole (formed in a supernova), a typical neutron star, a one-solar-mass white dwarf, main-sequence star of spectral type M, Jupiter, the Moon

What would you be most likely to find if you returned to the solar system in 10 billion years?

a white dwarf

The maximum mass of a white dwarf is ________.

about 1.4 times the mass of our Sun

The maximum mass of a white dwarf is _________.

about 1.4 times the mass of our Sun

What is the current limit to distances we can measure via parallax, until the results of the new Gaia mission become available?

about 1000 light years

This figure shows how the luminosity of supernovae change over time. How long does it take a white dwarf supernova to decrease in luminosity by a factor of 100 from its peak?

about 200 days

If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.

accelerate as you fall and cross the event horizon completely unhindered

Which model is most strongly supported by the data on the graph?

accelerating

Which model predicts the largest average distance between galaxies 6 billion years ago?

accelerating

Which of the models predict that galaxies should be getting farther apart now? (Keep in mind that now is located at at time = 0 years on the graph.) Check all that apply.

accelerating coasting critical recollapsing

The following diagrams represent a balloon analogy for the expansion of the universe. Each diagram shows two balloons: The small pink balloon represents the universe at an early time and the large red balloon represents the universe at some later time. The black dot on each balloon represents a galaxy. Rank the diagrams based on how much the galaxy has expanded in size (due to the overall universal expansion) from the early time to the later time in each case, from most expansion to least expansion. If you think that two (or more) of the diagrams show galaxies that have expanded by the same proportion, indicate this equality by dragging one diagram on top of the other(s).

all balloons in center (on top of each other) because galaxies aren't expanding

The gravitational lens effect has been verified by

all of the above

What are scientists' best guess(es) for the requirement(s) of life?

all of the above

Which of the following statements correctly summarize key differences between the disk and the halo?

all of them

According to our modern understanding, what is a nova?

an explosion on the surface of a white dwarf in a close binary system

Which of the following changes would cause the fusion rate in the Sun's core to increase?

an increase in the core temperature, a decrease in the core radius

What is the basic definition of a black hole?

an object with gravity so strong that not even light can escape

When a particle of ordinary matter meets its precise opposite particle of antimatter, the result is __________ with complete conversion of mass into energy.

annihilation

What do we need to measure in order to determine a star's luminosity?

apparent brightness and distance

The distribution of the dark matter in a spiral galaxy is

approximately spherical and about ten times the size of the galaxy halo

A typical white dwarf is _________.

as massive as the sun but only about as large as the Earth

If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.

at a constant, normal rate as you approach the event horizon

The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.

be an emission line spectrum

Why do disk stars bob up and down as they orbit the galaxy?

because the gravity of other disk stars always pulls them toward the disk

Now, let's turn our attention to rotation curves for orbiting masses which are not rigidly held together like the points on a merry-go-round. The Rotation Curve of the Solar System interactive figure shows the orbits of Mercury, Venus, Earth, and Mars. Click on each of the orbits, and watch the corresponding points appear on the graph below it. If a planet (or asteroid) orbited the Sun at three times the distance of Mars, its orbital speed would be __________.

between one-third and two-thirds the orbital speed of Mars

Which of the following layers of the Sun can be seen with some type of telescope? Consider all forms of light, but do not consider neutrinos or other particles.

chromosphere, photosphere, corona

Strong evidence for the existence of dark matter comes from observations of:

clusters of galaxies.

Listed following are three possible models for the long-term expansion (and possible contraction) of the universe in the absence of dark energy. Rank each model from left to right based on the ratio of its actual mass density to the critical density, from smallest ratio (mass density much smaller than critical density) to largest ratio (mass density much greater than critical density).

coasting universe, critical universe, recollapsing universe

The quantity called the "enclosed mass" M(<r) represents ALL of the mass inside radius r. If the enclosed mass M(<r) is constant with increasing radius, where is the mass?

concentrated in the center

The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust, protostar, main sequence g star, red giant, planetary nebula, white dwarf

Provided following are various stages during the life of a high-mass star. Rank the stages based on when they occur, from first to last.

contracting cloud of gas and dust, protostar, main-sequence star, red supergiant, supernova, neutron star

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

cooler and larger in radius

In which of the following layer(s) of the Sun does nuclear fusion occur?

core

Rank the following layers of the Sun based on the pressure within them, from highest to lowest.

core, radiation zone, convection zone, photosphere

Rank the following layers of the Sun based on their temperature, from highest to lowest.

core, radiation zone, convection zone, photosphere

Rank the layers of the Sun based on their density, from highest to lowest.

core, radiation zone, convection zone, photosphere, chromosphere, corona

Listed following are the different layers of the Sun. Rank these layers based on their distance from the Sun's center, from greatest to least.

corona, chromosphere, photosphere, convection zone, radiation zone, core

Observations of the __________ provide a way to test our theory of the Big Bang.

cosmic microwave background

Scientists investigating __________ study how the distribution of galaxies changes with time.

cosmology

The circular but relatively flat portion of the galaxy is the

disk

Our Sun belongs to the __________ of the Milky Way Galaxy.

disk component

The following diagrams are similar to those in Part A, except this time each one shows two galaxies: "your galaxy" and a second galaxy. Rank the diagrams based on how far the second galaxy has moved away from your galaxy due to expansion of the universe between the early time and the later time, starting at the left with the one that has moved the largest distance and moving to the one that has moved the smallest distance at the right.

dots farthest apart to dots closest together

The Rotation Curve for a Merry-Go-Round interactive figure shows a rotating merry-go-round. Click several points on the merry-go-round, and watch the corresponding points appear on the graph below it. This graph is what we call a rotation curve, because it plots the speed at which any point rotates around the center (the orbital speed) against the distance of that point from the center. Based on the graph, you can conclude that doubling the distance of a point from the center of the merry-go-round would __________.

double its orbital speed

The __________ is a single force that unifies the electromagnetic and weak forces.

electroweak force

A(n) ________ contains hot, ionized gas but very little cool gas or dust.

elliptical galaxy

Matter consisting of particles that differ from those found in atoms is generally referred to as __________ matter.

exotic (or nonbaryotic)

Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.

fainter and has most of its photons at longer wavelengths

Each data point represents a single white dwarf supernova that has been observed. The data points that appear farthest to the left on the graph represent the white dwarf supernovae that are the __________.

farthest away from us

Which of these groups of particles has the greatest mass?

four individual protons

The two facts from Parts C and D lead to the "inescapable conclusion" that individuals in a population will have unequal reproductive success, so that those whose traits best enable them to survive will leave more offspring. Therefore, in any local environment, over time, __________.

heritable traits that enhance survival will become progressively more common in succeeding generations

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

hotter and smaller in radius

In the past, the temperature of the universe was _____.

hotter than it is today

To calculate the dashed orbits from the stellar positions, astronomers had to assume that __________.

if they observed for many more years, the dots would trace out ellipses

According to current understanding, the two most abundant elements in the universe were made __________.

in the Big Bang

The Sun's location in the Milky Way Galaxy is _________.

in the galactic disk, roughly halfway between the center and the outer edge of the disk

Where does most star formation occur in the Milky Way Galaxy?

in the spiral arms

As the mass of the central star increases, the distance to the habitable zone __________ and the size (width) of the habitable zone __________.

increases / increases

Which forms of light are lower in energy and frequency than the light that our eyes can see?

infrared and radio

Telescopes designed to study the earliest stages in galactic lives should be optimized for observations in ______.

infrared light

According to the diagram, what is the most abundant element with an atomic number greater than or equal to 20?

iron

The type of galaxy known as a(n) __________ was more common in the universe 10 billion years ago.

irregular galaxy

We found that mass must be inferred for the star described in Part A. However, we can measure a star's mass directly if __________.

it is a member of an eclipsing binary system

How did oxygen (O2) get into Earth's atmosphere?

it was released by life though the process of photosynthesis

If we say that a galaxy has a lookback time of 1 billion years, we mean that _________.

its light traveled through space for 1 billion years to reach us

The total amount of power (in watts, for example) that a star radiates into space is called its _________.

luminosity

Listed following are several astronomical objects. Rank these objects based on their diameter, from largest to smallest. (Note that the neutron star and black hole in this example have the same mass to make your comparison easier, but we generally expect black holes to have greater masses than neutron stars.)

main-sequence star of spectral type A, Jupiter, a one-solar-mass white dwarf, the Moon, a two-solar-mass neutron star, the event horizon of a two-solar-mass black hole

Which of the following best summarizes what we mean by dark matter?

matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light

Current understanding holds that a galaxy's type (spiral, elliptical, or irregular) ______.

may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies

We can always determine the recession velocity of a galaxy (at least in principle) from its redshift. But before we can use Hubble's law, we must first calibrate it by __________.

measuring the distances to many distant galaxies with a standard candle technique

Which of the following is NOT one of the three main strategies used to measure the mass of galaxy clusters?

measuring the temperatures of stars in the halos of the galaxies

Which of the following is not one of the three main strategies used to measure the mass of a galaxy clusters?

measuring the temperatures of stars in the halos of the galaxies

7. Incoming ultraviolet light from the Sun can cause a __________ in a living organism's DNA that can affect its ability to survive and reproduce.

mutation

The notion that living organisms with advantages that give them greater reproductive success (in some local environment) will survive while others perish is an example of what Darwin called __________

natural selection

Click "show" for the emission line spectrum, then click "choose gases" and study the emission line spectrum for neon. The neon "OPEN" sign appears reddish-orange because __________.

neon atoms emit many more yellow and red photons than blue and violet photons

From Part E you know the mass of the central object. Now consider its size. Based on what you can see in the diagram, you can conclude that the diameter of the central mass is __________.

no more than about 70 AU

A white dwarf supernova leaves behind

nothing

Which two energy sources can help a star maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

The following four graphs are the same as those from Part D, with each showing a possible relationship for Hubble's law. Rank the graphs based on the prediction they each would make for the current age of the universe, from oldest to youngest.

opposite of previous

Measurements of how orbital speeds depend on distance from the center of our galaxy tell us that stars in the outskirts of the galaxy

orbit the galactic center just as fast as stars closer to the center

4. Matter made from atoms, with nuclei consisting of protons and neutrons, represents what we call __________ matter.

ordinary (or baryonic)

The diagram indicates that the third most abundant element in the Milky Way Galaxy is _____.

oxygen

Solar energy leaves the core of the Sun in the form of

photons

Which of the following lists the stages of life for a low-mass star in the correct order?

protostar, main-sequence star, red giant, planetary nebula, white dwarf

Astronomers are seeking to obtain an image of the region around the black hole's event horizon with a project called the Event Horizon Telescope. What type of light does this project seek to observe?

radio waves

Pulsars are thought to be _________.

rapidly rotating neutron stars

Which model is most clearly ruled out by the data on the graph?

recollapsing

Which of the models predict that galaxies will eventually get closer together in the future? Check all that apply?

recollapsing

Listed following are four models for the long-term expansion (and possible contraction) of the universe. Rank each model from left to right based on its prediction for the current age of the universe, from youngest to oldest.

recollapsing universe, critical universe, coasting universe, accelerating universe

Listed following are four models for the long-term expansion (and possible contraction) of the universe. Rank the models from left to right based on their predictions for the average distance between galaxies five billion years from now, from smallest to largest.

recollapsing universe, critical universe, coasting universe, accelerating universe

The __________ of spiral galaxies provide strong evidence for the existence of dark matter.

rotation curves

As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________.

slows down as it approaches the event horizon, and never actually crosses the event horizon

The first of the two "undeniable facts" is that any localized population of a species has the potential to produce far more offspring than the local environment can support. This fact is important to understanding evolution because it means that __________.

some individuals possess traits that make them better able than others to compete for food and other resources

The second of the two "undeniable facts" is that individuals in a population of any species vary in many heritable traits (traits passed from parents to offspring), so that no two individuals are exactly alike. This fact is important to understanding evolution because it means that __________.

some individuals possess traits that make them better able than others to compete for food and other resources

From Part A, you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a star's surface temperature?

spectral type

A ________ stands out in a photo of a galaxy because it shines brightly with light from massive young stars and glowing clouds of gas and dust.

spiral arm

Our Milky Way galaxy is a

spiral galaxy

The Milky Way is a(n) __________.

spiral galaxy

The enclosed mass M(<r) represents ALL of the mass inside the radius r. If the enclosed mass M(<r) increases out to larger radii, where is the mass?

spread out over a large range of radii

From Part D, you know that the galaxy's rotation curve is nearly flat, even well beyond the point at which we see any stars in the galaxy. According to the law of gravity as we understand it today, the only explanation for these this flatness is that __________.

substantial amounts of mass must reside at great distances from the galactic center

Radar, the first link in the cosmic distance chain, is used to establish the baseline distance necessary for the second link, parallax. What baseline distance must we know before we can measure parallax?

the Earth-Sun distance

Which of the following worlds is not considered a candidate for harboring life?

the Moon

Measuring the amount of deuterium in the universe allows us to set a limit on _________.

the density of ordinary (baryonic) matter in the universe

Hubble's law expresses a relationship between __________.

the distance of a galaxy and the speed at which it is moving away from us

Notice that some of the stars on the diagram are represented by a series of dots that are very close together, while others have their dots farther apart. Keeping in mind that all the stellar positions were measured at approximately one-year intervals, which stars are moving the fastest in their orbits during the time period indicated by the dots? The fastest stars are the ones with...

the dots farthest apart

Which of the following is not evidence for dark matter?

the expansion of the universe

In the Drake equation (Number of Civilizations = NHP × flife × fciv × fnow), what do we mean by fnow?

the fraction of planets with civilizations at the present time (as opposed to only in the past or future)

What is the Big Bang theory?

the idea that all matter and energy in the universe began in an unimaginably dense state, and then space itself began expanding

To understand why the galaxy rotation curve in Part D is flat, we must first understand how gravity determines the orbital speeds of stars around the galactic center. Consider any star on a circular orbit around the center of the galaxy. The speed of the star's orbit depends on the star's distance from the galactic center and __________.

the mass of the galaxy that resides within the star's orbit

What two observable properties of a Cepheid variable are directly related to one another?

the period between its peaks of brightness and its luminosity

We can in principle measure the expansion rate by studying galaxies in many different directions in space and at different times of year. If we compare such observations, we would find that the expansion rate is __________.

the same no matter when or in which direction we measure it

Listed following are several astronomical objects. Rank these objects based on their density, from highest to lowest.

the singularity of a black hole, a typical neutron star, a one-solar-mass white dwarf, a main-sequence star

Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 73 hours the star becomes dimmer for about 2 hours. The change in brightness alternates between a small change and a large change. The most likely explanation is that ________.

the star is a member of an eclipsing binary star system

What can we learn about a star from a life track on an H-R diagram?

the surface temperature and luminosity the star will have at each stage of its life

What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?

the time between eclipses and the average distance between the stars

Consider a distant galaxy located directly behind a cluster of galaxies as shown in this interactive figure. Knowing the distance to the cluster of galaxies and the angular separation of the lensed images of the distant galaxy, astronomers can estimate:

the total amount of matter in the cluster of galaxies, including both dark matter and matter in stars

Which of the following does inflation help to explain?

the uniformity of the cosmic microwave background

Consider this statement from Part A: "Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that __________.

the universe began very hot and dense and has been cooling as it expands

Based on what you've learned from the raisin cake analogy, which two properties of distant galaxies do astronomers have to measure to show that we live in an expanding universe?

their distances and speeds

What characteristics of the orbiting stars do we need to measure in order to calculate the mass of the central object, Sgr A*?

their orbital periods and average orbital distances

One of the key premises for the __________ is that living organisms are able to produce far more offspring than their environment can support.

theory of evolution

The first of the two "undeniable facts" is that any localized population of a species has the potential to produce far more offspring than the local environment can support. This fact is important to understanding evolution because it means that __________.

there is competition for survival among the individuals of the population

Careful measurements show that the hot, X-ray-emitting gas in the Bullet Cluster contains about 7 times as much total mass as all the stars in the cluster's galaxies combined. Therefore, the fact that the most of the gravity is in the blue regions that surrounds the visible galaxies, rather than in the regions with the hot gas, indicates that __________.

there is even more matter surrounding the galaxies than there is in the hot gas

Most interstellar clouds remain stable in size because the force of gravity is opposed by _______ within the cloud.

thermal pressure

One of the inferred statements from Part A is that "Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact that the cosmic microwave background exhibits __________.

tiny temperature variations in different directions

Shown following are several times in the history of the universe. Rank these times from left to right based on the average temperature of the universe at each time, from coolest to hottest.

today, 1.5 billion years after the Big Bang, 100 million years after the Big Bang, 1 million years after the Big Bang, 500,000 years after the Big Bang

A GUT (grand unified theory) refers to theories that

unify the strong force and the electromagnetic and weak forces.

A "GUT" (grand unified theory) refers to theories that _________.

unify the strong force with the electromagnetic and weak nuclear forces

Dark matter is inferred to exist because:

we can observe its gravitational influence on visible matter.

Using the technique of main-sequence fitting to determine the distance to a star cluster requires that ________.

we have telescopes powerful enough to allow us to identify the spectral types of main-sequence stars of many masses in the cluster

A white dwarf is ________.

what most stars become when they die

When does a protostar become a main-sequence star?

when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space

You have a time machine with a dial that you can spin to send you randomly to any time in Earth's history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you?

you'll suffocate because you'll be unable to breathe the air

The theory of evolution by natural selection gained rapid acceptance among biologists after Darwin published it in 1859, in part because it was so successful in explaining what we see in the fossil record. The theory of evolution has gained even further support since that time, because it has successfully passed many other observational tests. Which of the following statements represent successful tests of the theory of evolution by natural selection?

•Over time, bacteria tend to acquire resistance to antibiotic drugs. •Species often show unique adaptations that are suited to the specific environment in which they live and might be detrimental in other environments. •Genetic comparisons show that the DNA of closely related species is more similar than that of more distantly related species.